BACKGROUND: The double-blind placebo-controlled design is commonly considered the gold standard in research methodology; however, subject expectation bias could subvert blinding. OBJECTIVE: The primary aim of this study was to examine the impact of expectation bias. Specifically, we examined perceived treatment assignment on smoking cessation outcome rates among participants enrolled in a clinical trial of bupropion (150 mg SR, BID). DESIGN: Analyses were conducted on data collected during "Kick It at Swope," a double-blind, placebo-controlled, randomized trial of 600 African-American smokers. Chi-square and multiple logistic regression analyses were used to examine the impact of perception of assignment on treatment effect and cotinine-verified smoking abstinence rates. PARTICIPANTS: Participants were predominantly middle-aged (mean 44.7, SD 11.2), African-American women (68.6%), who smoked 19 CPD (SD=8.1). Most had completed at least a high school education or GED (51.6%), and 55% had a monthly family income <$1,800. MEASUREMENTS: At week 6 (end of treatment) and week 26 (end of study), participants were asked to report their perceived treatment group assignment. Self-reported abstinence (weeks 6 and 26) was confirmed using CO and cotinine biochemical verification. RESULTS: After adjusting for actual treatment assignment, age and baseline cotinine, participants who perceived being assigned to bupropion vs. placebo were more likely to be abstinent at weeks 6 (OR=2.07, 95% CI: 1.29 to 3.33, p= 0.002) and 26 (OR=1.85, 95% CI: 1.05 to 3.24, p= 0.032). CONCLUSIONS: Results support previous research that expectation bias associated with judgment of treatment assignment is a strong predictor of outcome and confirms this relationship in a smoking cessation trial using bupropion SR among African-American smokers.
Bibliographical noteFunding Information:
Acknowledgements: This study was funded by grant R01CA77856 from the National Cancer Institute. GlaxoSmithKline provided study medication (both active and placebo) but played no role in the design, conduct of the study, or interpretation and analysis of the data. We thank the staff and participants at Swope Parkway Health Center for making this research possible.
Copyright 2009 Elsevier B.V., All rights reserved.
- African American
- Expectation bias
- Placebo effect
- Smoking cessation